My grievance is that too many people prescriptively advocate for descriptivism by insisting that the rules of grammar not be followed, even if the work concerned will be subject to scrutiny under the academic standards of higher education.
1) Languages should become more explicitly defined as they evolve and expand over time, not more vague, not less structured, nor less differentiated across similar but not identical meanings. New rules must necessarily be agreed upon as new and more precise language comes into use. The whole point of language is to communicate in a way that promotes a more accurate understanding of each other. We already have a perfectly relate-able way of communicating feelings to each other, it's called art. And, sure, language can be applied as a medium of art, as well; However, language is also unique its ability to exemplify specificity. It has more applications to be used for many purposes so berating the one feature unique to it seems a bit stubborn and pedantic itself.
2) Advising people who have bothered to come here, register an account, and ask a specific question regarding English grammar are obviously interested in knowing what the answer is in terms of the academic standard of higher education. If a person is in a casual enough situation where correctness of grammar is not an issue, then they wouldn't be prompted to ask about what the grammatically correct way of saying something is, in the first place. In other words, any suggestion to disregard proper grammar and just write how you speak is directly equatable to willfully sabotaging someone's term paper or college thesis, and kind of like being a jerk, if you ask me.
3) Why must self-described descriptivist linguists butt their noses into questions specifically about the proper use grammar? If all they are out to do is describe what is and not participate in or influence the development of a more conformed, specific, complex, and yet more widely understood, language standard... then why should questions about actual grammar be of the least bit of interest to them? Why not just keep their opinions about language theory to themselves and let the prescriptivist grammarians answer questions that are asking about the prescribed use of grammar?
I'm not against anyone who wants analyze modern conversational speech - go ahead, analyze and describe all you want... in the domain of cultural linguistic discussions and/or philosophical conversations; But, when it comes to questions regarding the proper use of grammar, sentence structure, or the parts of speech (questions which are clearly seeking advise from actual educators and not the contemplative notions of language theorists) - Well, couldn't you just take a pass on those questions?
P.S. How on earth can people possibly convince themselves that stripping away the scaffolding which lends shape to something and tossing the rest into one, big, free-flowing blob of mix-and-match sentence fragments and generalizations into a pile, on the floor - that that somehow qualifies as being the more scientific of the two approaches to language? Scientific methods are strictly devised within the most restrictive of parameters obtainable with every little detail of every little itemized protocol being followed, diligently. So how exactly is descriptivism in any way scientific?. Disregarding any portion of a set of predetermined instructions (a.k.a. rules) is the most unscientific way to go about making reliable observations. Scientific = conformity to standards, regardless of whether you like those standards. So, please, just stop saying that?